This application relates to a new class of nonionic polyurethanes useful for thickening a wide range of aqueous systems, and more particularly relates to relatively low molecular weight thickeners, characterized by hydrolytic stability, versatility and efficiency, and to a wide vareity of aqueous systems containing the thickeners.
Since ancient times additives have been sought for aqueous systems to increase the viscosity and to maintain the viscosity at required levels under specified processing conditions and end use situations. For this reason such additives are commonly called "thickeners", although the additives often impart or improve other properties as well in a particular system. For example, thickeners are used in latex paints not only for viscosity improvement and control, but also for protective colloidal action and for improvement of pigment suspension, leveling and flow. In addition, the additives often emulsify, disperse and stabilize latex ingredients and are themselves film formers. Such additives, especially in latex paint and textile treating compositions, improve the "sticking" or binding properties of the composition. In water-based coloring compositions, such as pigment printing pastes and acid dye baths, thickeners are utilized for their suspending properties. In textile treating compositions, thickeners are sought which also improve softening, sizing and handling properties. Thickeners are commonly used in cosmetics for thixotropy and to improve body, smoothness and silkiness. As additives to paper coating compositions, thickeners improve thickening under high shear conditions. Thickeners are likewise useful for the foregoing and other properties in oil well drilling and flooding fluids, fire-fighting foams and fluids, detergents, leather pastes and finishes, adhesives, pharmaceuticals, agricultural formulations, and emulsions of all kinds. The list of applications and auxiliary properties of thickeners is virtually endless.
Among the many well-known thickeners may be mentioned natural products such as the alginates, casein, gum karaya, locust bean gum and gum tragacanth, and modified natural products such as the cellulosics, including methyl cellulose, hydroxethyl cellulose and hydroxypropylmethyl cellulose. Totally synthetic thickeners are also available, such as carboxy vinyl ether copolymers, acrylic polymers and maleic anhydridestyrene copolymers. However, all of the known thickeners have deficiencies.
For example, most latex paints are neutral or mildly alkaline and contain various electrolytes. Ionic thickeners are undesirable in such paints because the rheology they impart to the paints is unduly sensitive to pH and to the other ionic ingredients. Ionic thickeners normally are not used at all in paint latices containing polyvalent cations because the latex thereby becomes unstable and any improvement in viscosity achieved by their use will rapidly be lost. Moreover, dried films of latex paints containing ionic thickeners are sensitive to water and to alkaline solutions, and tend to adhere poorly to alkaline substrates such as concrete and mortar. Other thickeners are water and alcohol sensitive, impart poor rheology (such as spatter or ropiness) or are inefficient, requiring unduly high concentrations for effective viscosity improvement and control. Still other thickeners cannot be used in textile treating compositions because of a tendency to impart an undue harshness to the textile. The natural or modified natural thickeners are easily contaminated by various microbial species or are enzymatically degraded and systems containing them therefore require antimicrobial agents or other controls.
The thickeners of the invention exhibit significant improvements over the foregoing and other known thickeners, such as the thickeners disclosed in U.S. Pat. No. 3,770,684 to Singer et al. and in German Pat. No. 2,054,885 assigned to BASF. It could not have been predicted from these patents, for example, that relatively minor amounts (about 1%) of the polymers of this invention would increase the viscosity of water to 1000 cps or more. More importantly, the thickeners of the invention are exceptionally versatile in their ability to impart the special rheological control required in diverse types of thickened systems. Such control is achieved by selecting thickeners and blending them with various aqueous systems in fashions not taught by the prior art.
The thickeners of this invention provide a combination of properties not found in any one class of known thickeners. For example, they are nonionic and in many cases are highly efficient viscosity improvers although having a relatively low molecular weight. They are stable to water and alcohol and are not sensitive to biodegradation. They are versatile in that not only do they thicken virtually unlimited types of aqueous systems, but they also impart many of the auxiliary properties described above. Thus, as additives to textile binder compositions, they actually soften rather than harden the fabric. In latex paints, especially, they not only thicken but in many cases also provide superior flow and leveling, and give excellent viscosity control under both low and high shear conditions.